Dual stage cryocooler

Abstract

A cryoablation tool has a primary fluid circuit for cryogenically cooling or heating tissue surrounding the distal portion of the cryoablation tool. The primary fluid circuit has a primary-primary heat exchanger facilitating recuperative heat exchange between a high pressure stream of a primary fluid and a low pressure stream of the primary fluid. The cryoablation tool has a secondary fluid circuit having a secondary-secondary heat exchanger for permitting recuperative heat exchange between a high pressure stream of a secondary fluid and a low pressure stream of the secondary fluid. The secondary fluid circuit also has a primary-secondary heat exchanger permitting heat exchange between the high pressure stream of the primary fluid and the low pressure stream of the secondary fluid.

We claim: 
     
       1. A cryoablation tool comprising:
 a shaft having a proximal end and a distal end; 
 a primary supply conduit configured to supply a primary fluid from a high-pressure cryogenic gas source to a distal end of the shaft, the primary supply conduit comprising a first Joule-Thomson (J-T) orifice, configured to deliver the primary fluid to a first expansion chamber; 
 a primary return conduit configured to carry the primary fluid away from the first expansion chamber; 
 a secondary supply conduit configured to supply a secondary fluid to a second J-T orifice, the second J-T orifice configured to deliver the secondary fluid to a second expansion chamber; and 
 a secondary return conduit configured to carry the secondary fluid away from the second expansion chamber, 
 the primary supply conduit comprising a primary-secondary heat exchange region and a primary-primary heat exchange region, the primary-primary heat exchange region being down stream of the primary-secondary heat exchange region; and the secondary supply conduit comprising a secondary-secondary heat exchange region up stream of the second J-T orifice, and 
 the primary return conduit further configured to pass the primary fluid over the primary-primary heat exchange region, in counterflow to the supply direction; the secondary return conduit further configured to pass the secondary fluid sequentially over the primary-secondary heat exchange region and the secondary-secondary heat exchange region in counterflow to the supply direction. 
 
     
     
       2. The cryoablation tool according to  claim 1 , wherein the secondary return conduit is configured to pass the secondary fluid sequentially over a full length of the primary-secondary heat exchange region before passing the secondary fluid over a full length of the secondary-secondary heat exchange region. 
     
     
       3. The cryoablation tool according to  claim 1 , wherein the secondary-secondary heat exchange region and primary-secondary heat exchange region are arranged within the secondary return conduit and the secondary-secondary heat exchange region is arranged downstream to the primary-secondary heat exchange region with respect to a flow direction within the secondary return conduit. 
     
     
       4. The cryoablation tool according to  claim 1 , wherein the primary supply conduit comprises a tubular region wound in a series of turns about a mandrel to form the primary-secondary heat exchanger, and the secondary supply conduit comprises a tubular region wound in a series of turns about the same mandrel to form the secondary-secondary heat exchanger. 
     
     
       5. The cryoablation tool according to  claim 1 , wherein the primary return conduit is configured to pass the primary fluid over the primary-primary heat exchange region but not the primary-secondary heat exchange region or the secondary-secondary heat exchange region. 
     
     
       6. The cryoablation tool according to  claim 1 , the primary return conduit is configured to pass the primary fluid over the primary-primary heat exchanger; and the secondary return conduit is configured to pass the secondary fluid over the primary-secondary heat exchanger prior to passing the secondary fluid over the secondary-secondary heat exchanger. 
     
     
       7. The cryoablation tool according to  claim 1 , wherein the primary supply conduit is arranged in a first plurality of coils, configured as a primary-secondary heat exchanger within the primary-secondary heat exchange region and a second plurality of coils, configured as a primary-primary heat exchanger, within the primary-primary heat exchange region; and the secondary supply conduit being arranged in a third plurality of coils configured as a secondary-secondary heat exchanger within the secondary-secondary heat exchange region. 
     
     
       8. The cryoablation tool according to  claim 7 , wherein the first plurality of coils comprises a first coil and a second coil, the first coil arranged upstream of the second coil relative to the direction of primary fluid flow through the first coil; each coil of the second plurality of coils being positioned downstream of the said second coil relative to the direction of primary fluid flow in the first coil; and each coil of the third plurality of coils is positioned upstream of the first coil relative to the direction of primary fluid flow in the said first coil. 
     
     
       9. The cryoablation tool according to  claim 1 , wherein the secondary return conduit is configured to pass the secondary fluid sequentially over a full length of the primary-secondary heat exchange region before passing the secondary fluid over a full length of the secondary-secondary heat exchange region, the secondary return conduit is configured to pass the secondary fluid over each coil of the primary-secondary heat exchanger before passing it over the secondary to secondary heat exchanger. 
     
     
       10. The cryoablation tool according to  claim 1 , wherein the primary-primary heat exchange region is arranged within the primary return conduit and is further, arranged distally of both the primary-secondary and the secondary-secondary heat exchange regions. 
     
     
       11. The cryoablation tool according to  claim 1 , wherein the secondary-secondary heat exchange region is arranged proximally to the primary-secondary heat exchange region, within the secondary return conduit. 
     
     
       12. The cryoablation tool according to  claim 1 , wherein the primary supply conduit comprises a tubular region wound in a series of turns about a mandrel to form the primary-secondary heat exchanger, the secondary supply conduit may comprise a tubular region wound in a series of turns about a mandrel to form the secondary-secondary heat exchanger, the primary supply conduit may comprise a tubular region wound in a series of turns about a mandrel to form the primary-secondary heat exchanger, and the secondary supply conduit may comprise a tubular region wound in a series of turns about the same mandrel to form the secondary-secondary heat exchanger; the primary supply conduit may comprise a tubular region wound in a series of turns about a mandrel to form the primary-primary heat exchanger. 
     
     
       13. The cryoablation tool according to  claim 1 , wherein the primary-secondary heat exchange region and the secondary-secondary heat exchange region are each disposed within the secondary return conduit; the secondary return conduit may then fluidly isolate the primary return conduit from the primary-secondary heat exchange region and the secondary-secondary heat exchange region. 
     
     
       14. The cryoablation tool according to  claim 1 , wherein the primary return conduit comprises a portion disposed concentrically about the secondary return conduit, the portion is downstream of the primary-primary heat exchange region with respect to the direction of expanded primary fluid flow. 
     
     
       15. The cryoablation tool according to  claim 1 , wherein the primary return conduit is configured to vent the primary fluid to atmosphere and/or the secondary return conduit is configured to vent the secondary fluid to atmosphere. 
     
     
       16. A cryoablation method using a cryoablation tool with a shaft having arranged therein a primary supply conduit connected to a first Joule-Thomson (J-T) orifice in a first expansion chamber and a secondary supply conduit connected to a second J-T orifice in a second expansion chamber, the method comprising:
 supplying a primary fluid from a high-pressure cryogenic gas source to a distal end of the shaft; 
 expanding, cryogenically, a high-pressure stream of a primary fluid to a low-pressure stream of the primary fluid via the primary fluid circuit, the first J-T orifice being fluidly coupled to a primary-primary heat exchanger via a primary supply conduit to receive the high-pressure stream of the primary fluid after the high-pressure stream of the primary fluid passes through the primary-primary heat exchanger; 
 directing the primary fluid away from the first expansion chamber via a primary return conduit arranged within the shaft; 
 directing a low-pressure stream of a secondary fluid to exchange heat with a high-pressure stream of a primary fluid in a primary-secondary heat exchanger prior to exchanging heat with the high-pressure stream of the secondary fluid in a secondary-secondary heat exchanger; 
 directing the secondary fluid leaving the secondary-secondary heat exchanger to enter a secondary conduit and to flow toward the second J-T orifice; and 
 directing the secondary fluid away from the second expansion chamber via a secondary return conduit arranged within the shaft. 
 
     
     
       17. The method of  claim 16 , further comprising directing, via the secondary return conduit, the secondary fluid sequentially over the primary-secondary heat exchanger and the secondary-secondary heat exchanger in counterflow to the supply direction in each case. 
     
     
       18. The method of  claim 16 , further comprising upon expansion, directing the low-pressure stream of the secondary fluid to flow over finned portions of the primary-secondary heat exchanger for recuperative heat exchange with the high-pressure stream of the primary fluid. 
     
     
       19. The method of  claim 18 , further comprising directing the low-pressure stream of the secondary fluid to flow over a finned portion of the secondary-secondary heat exchanger for recuperative heat exchange with the high-pressure stream of the secondary fluid. 
     
     
       20. The method of  claim 16 , wherein the secondary fluid is prioritized to flow first through the primary-secondary heat exchanger such that the secondary fluid is coldest when in heat exchange with the primary fluid, thereby permitting optimal heat removal from the primary fluid for effective precooling of the primary fluid.